Comb drive for microelectromechanical system

Abstract

A comb drive for MEMS device includes a stator and a rotor displaceable relative to the stator in a first direction. The stator includes stator comb fingers and the rotor includes rotor comb fingers. The stator comb fingers are coupled to two high impedance nodes to form high impedance node domains arranged in the first direction. The rotor comb fingers are coupled to two oppositely biased electrodes to form oppositely biased domains. Pairs of capacitors with opposite acoustic polarity are respectively formed between the high impedance node domains and the oppositely biased domains. The comb drive of the present invention has increased electrostatic sensitivity for a given unit cell cross-sectional area whilst maintaining an acceptable capacitance and linearity of voltage signal vs displacement. Extra force shim unit cells may be used, which allows for the stiffness between the rotor and stator to be controlled and reduced to zero for a particular displacement range, without impacting sensitivity.

What is claimed is: 
     
       1. A comb drive for microelectromechanical system (MEMS) device comprising a first set of comb fingers and a second set of comb fingers displaceable relative to each other,
 wherein one of the first set of comb fingers is coupled to a high impedance node (HIN) and another of the first set of comb fingers is coupled to another separate and independent HIN to form at least two HIN domains alternatingly arranged in a first direction; 
 one of the second set of comb fingers is coupled to a biased electrode and another of the second set of comb fingers is coupled to another biased electrode with opposite polarity to the biased electrode, to form at least two oppositely biased domains alternatingly arranged in the first direction; and 
 pairs of capacitors with opposite acoustic polarity within each pair are respectively formed between the at least two HIN domains and the at least two oppositely biased domains. 
 
     
     
       2. The comb drive of  claim 1 , wherein the at least two HIN domains and the two oppositely biased domains are arranged without overlapping in the first direction at a rest position where no voltage is applied to the comb drive. 
     
     
       3. The comb drive of  claim 1 , wherein the first set comb fingers extend along a second direction which is perpendicular to the first direction. 
     
     
       4. The comb drive of  claim 3 , wherein the biased domains each comprises a rectangular cross section perpendicular to the second direction, the rectangular cross section comprises a height dimension parallel to the first direction and a width dimension perpendicular to the first direction and the second direction, and the height dimension is less than the width dimension. 
     
     
       5. The comb drive of  claim 1 , wherein the number of the HIN domains is less than that of the biased domains, and the comb drive further comprises additional biased electrodes mounted to the stator. 
     
     
       6. The comb drive of  claim 1 , wherein the comb drive further comprises an additional cell that has a purpose of providing a positive stiffness contribution to the comb drive using biased rotor electrodes of alternating polarity and grounded stator electrodes. 
     
     
       7. The comb drive of  claim 1 , wherein the comb drive further comprises an additional cell that has a purpose of providing a positive stiffness contribution to the comb drive using biased rotor electrodes of same polarity and grounded stator electrodes. 
     
     
       8. The comb drive of  claim 1 , wherein the comb drive further comprises an additional cell that has a purpose of providing a positive stiffness contribution to the comb drive using biased rotor electrodes of alternating polarity and biased stator electrodes of alternating polarity. 
     
     
       9. The comb drive of  claim 1 , wherein the comb drive further comprises an additional cell that has a purpose of providing a negative stiffness contribution to the comb drive using biased rotor electrodes of alternating polarity and grounded stator electrodes. 
     
     
       10. The comb drive of  claim 1 , wherein the comb drive further comprises an additional cell that has a purpose of providing a negative stiffness contribution to the comb drive using biased rotor electrodes of same polarity and grounded stator electrodes. 
     
     
       11. The comb drive of  claim 1 , wherein the comb drive further comprises an additional cell that has the sole purpose of providing a negative stiffness contribution to the comb drive using biased rotor electrodes of alternating polarity and biased stator electrodes of alternating polarity. 
     
     
       12. The comb drive of  claim 1 , wherein the biased electrode and the another biased electrode have equal voltage magnitude. 
     
     
       13. The comb drive of  claim 1 , wherein the biased electrode and the another biased electrode have different voltage magnitude. 
     
     
       14. The comb drive of  claim 1 , wherein the first set of comb fingers are stator comb fingers and the second set of comb fingers are rotor comb finger; or
 the first set of comb fingers are rotor comb fingers and the second set of comb fingers are stator comb finger. 
 
     
     
       15. A divider circuit of a comb drive comprising:
 a first HIN and a second HIN where a voltage signal is output differentially therebetween; 
 a first pair of capacitors with opposite acoustic polarity formed between the first HIN and two oppositely biased electrodes respectively; and 
 a second pair of capacitors with opposite acoustic polarity formed between the second HIN and the two oppositely biased electrodes respectively.